This disclosure is directed to a method and apparatus for controlling the production of pitch. More particularly, the invention is directed to a method and apparatus for automatically controlling the production of pitch by measuring the temperature of the pitch at a preselected viscosity value, comparing this measured temperature value with a predetermined temperature value, and adjusting the parameters of the pitch process in response thereto.
Coal tar pitches (solid or semisolid residues remaining from the distillation of coal tars) and petroleum based pitches have found wide use in various industries. They have been used for many years as waterproofing agents and protecting coatings. Some examples of these uses include built-up roofings, foundation wall coatings, pipeline enamels, and many others. The pitches are usually applied in these uses as a hot melt. Some other important uses of pitches are as binders for paving materials, binders for electrodes for the aluminum and steel industries and as binders for a variety of other carbon products.
Each pitch has well defined characteristics and properties dictated generally by the end use which they are designed to serve. Normal coal tar pitches usually have softening points of at least about 40.degree. C and they may be as high as 135.degree. C or higher.
The pitches of different softening points are generally prepared by subjecting the crude tar pitches to a heat treatment or to a heat treatment in combination with various chemical reactants such as oxygen or air. The most common method of preparing pitches of different softening points is distillation.
Heretofore, the production of pitches having different softening points was controlled by a totally manual process. After selection of a suitable tar source and distillation conditions (temperature and pressure) continuous or batch pitch still operations are controlled by the softening point of the pitch product. In general, a customer specifies a certain softening point (by the ring and ball, or similar method) with a latitude of plus or minus 2.degree. to 3.degree. C. The still operator adjusts the controls according to the desired softening point of the product. This involves taking a sample from the still, preparing it for the softening point determination, carrying out the latter, comparing the softening point to the desired softening point, and adjusting the controls according to the comparison value. It takes from about 30 minutes to one hour to take the softening point, make the comparison and adjust the controls. After adjustments, it takes at least another half hour or so before the reaction mixture comes to equilibrium and another sample can be taken. Because of the inherent difficulties with the prior art method, there has been a desire in the industry for a better method and apparatus for controlling pitch still operations.